Generally, gypsum products do not have sufficient water resistance to allow them to be used in a “near-water” place where they might be in contact with water.
However, because there is a need to use a gypsum product in such a near-water place, research has been conducted to find a method to give water repellency to a gypsum product so that it can be used in a near-water place. In a proposed method, a water repellent such as a silicone oil or wax, or a water-repellent adjuvant that efficiently enhances the performance of a water repellent is added to gypsum slurry to give water repellency.
For example, Patent Document 1 discloses a method of waterproofing a gypsum product where at least one type of compound including polysiloxane and at least one type of compound including pregelatinized starch (a starch) are added to a plaster composition.